2020 AMC 8 Problems/Problem 13

1 Problem 13
2 Solution 1
3 Solution 2 (variant of Solution 1)
4 Solution 3 (non-algebraic)
5 Video Solution by NiuniuMaths (Easy to understand!)
6 Video Solution by Math-X (First understand the problem!!!)
7 Video Solution (🚀Very Quick🚀)
8 Video Solution by North America Math Contest Go Go Go
9 Video Solution by WhyMath
10 Video Solution
11 Video Solution by Interstigation
12 See also

Problem 13

Jamal has a drawer containing $6$ green socks, $18$ purple socks, and $12$ orange socks. After adding more purple socks, Jamal noticed that there is now a $60\%$ chance that a sock randomly selected from the drawer is purple. How many purple socks did Jamal add?

$\textbf{(A) }6 \qquad \textbf{(B) }9 \qquad \textbf{(C) }12 \qquad \textbf{(D) }18 \qquad \textbf{(E) }24$

Solution 1

After Jamal adds $x$ purple socks, he has $(18+x)$ purple socks and $6+18+12+x=(36+x)$ total socks. This means the probability of drawing a purple sock is $\frac{18+x}{36+x}$ , so we obtain $\frac{18+x}{36+x}=\frac{3}{5}$ Since $\frac{18+9}{36+9}=\frac{27}{45}=\frac{3}{5}$ , the answer is $\boxed{\textbf{(B) }9}$ .

Solution 2 (variant of Solution 1)

As in Solution 1, we have the equation $\frac{18+x}{36+x}=\frac{3}{5}$ . Cross-multiplying yields $90+5x=108+3x \Rightarrow 2x=18 \Rightarrow x=9$ . Thus, Jamal added $\boxed{\textbf{(B) }9}$ purple socks.

Solution 3 (non-algebraic)

$6$ green socks and $12$ orange socks together should be $100\%-60\% = 40\%$ of the new total number of socks, so that new total must be $\frac{6+12}{0.4}= 45$ . Therefore, $45-6-18-12=\boxed{\textbf{(B) }9}$ purple socks were added.

Video Solution by NiuniuMaths (Easy to understand!)

https://www.youtube.com/watch?v=bHNrBwwUCMI

~NiuniuMaths

Video Solution by Math-X (First understand the problem!!!)

https://youtu.be/UnVo6jZ3Wnk?si=6Ux3fNTMn5tSUnP3&t=1833

~Math-X

Video Solution (🚀Very Quick🚀)

https://youtu.be/0nnyYRYi-40

~Education, the Study of Everything

Video Solution by North America Math Contest Go Go Go

https://www.youtube.com/watch?v=u81EWYcC0Wg

~North America Math Contest Go Go Go

Video Solution by WhyMath

https://youtu.be/x9Di0yxUqeU

~savannahsolver

Video Solution

https://youtu.be/xjwDsaRE_Wo

Video Solution by Interstigation

https://youtu.be/YnwkBZTv5Fw?t=546

~Interstigation

2020 AMC 8 (Problems • Answer Key • Resources)
Preceded by Problem 12	Followed by Problem 14
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